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The theoretical and experimental basis for the development of a new dating technique using beta-gradient isochrons and ESR is presented. For uranium-free portions of enamel adjacent to sediment, we can determine a beta-dose gradient due to sources in the nearest 2 mm layer of the sediment. If the equivalent dose to successive layers of enamel is plotted against the beta dose rate to each layer, an estimate of the age (equal to the slope of the line) that depends only on the environmental beta dose rate can be determined. Experimental methods and results for four teeth are discussed. The significance of this approach lies in its ability to isolate an age estimate that is independent of the uranium uptake model, since only portions of the enamel which are far away enough from internal sources of uranium, such as dentine, are used. In addition, this technique provides a time-averaged estimate of the actual gamma plus cosmic dose rate provided that a reasonable estimate of the average moisture content is used to calculate the environmental beta dose rate. 相似文献
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Human tooth enamel powders, unheated as well as heated prior to X -irradiation at room temperature, have been investigated by means of Q - and W -band Electron Paramagnetic Resonance (EPR). Upon irradiation of enamel, carbonate-derived radicals are generated. The simplest acquired EPR spectra in this study consist mainly of a group of three different \hbox{CO}_3^{3-} signals, with a very weak \hbox{CO}_2^{-} contribution. The characterisation of the paramagnetic species in enamel is quite important for the reliability of EPR applications ( e.g. , EPR retrospective dosimetry). The spectra from the heated samples reveal a striking resemblance with spectra from certain irradiated synthetic apatite powders. The spin Hamiltonian parameters obtained from the computer simulations of the Q - and W -band spectra are compared with those reported in the literature. 相似文献
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利用FTIR与XRD判断成都金沙遗址古人类与古动物牙齿釉质和牙本质中羟基磷灰石受埋藏环境和成岩作用的污染程度。XRD图谱结果反映牙釉质和牙本质样品中最主要成分是羟基磷灰石,但衍射峰宽,且部分重叠,表明羟基磷灰石结晶度差。所有样品FTIR图谱中H2O和OH-的振动带显著,PO3-4和CO2-3主要振动带的特征峰明显,近似现代生物羟基磷灰石。表征羟基磷灰石结晶程度的PCI指数值在2.4至4.0之间,同时利用BPI指数估算的羟基磷灰石中CO2-3含量较高, 说明样品结晶程度不高。上述结果表明,所取的金沙遗址古人类与古动物牙釉质和牙本质中羟基磷灰石受埋藏和成岩作用的污染小。 相似文献